misc/cgo: fix test on iOS

The test in CL 123715 doesn't work on iOS, it needs to use a different
version scheme to determine whether SecKeyAlgorithm and friends exist.
Restrict the old version test to OSX only.

The same problem occurs on iOS: the functions tested don't exist before
iOS 10.  But we don't have builders below iOS 10, so it isn't a big issue.
If we ever get older builders, or someone wants to run all.bash on an
old iOS, they'll need to figure out the right incantation.

Update #24161
Update #26355

Change-Id: Ia3ace86b00486dc172ed00c0c6d668a95565bff7
Reviewed-on: https://go-review.googlesource.com/123959
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/cgo/test/issue24161e0/main.go

@@ -9,9 +9,10 @@ package issue24161e0
 /*
 #cgo CFLAGS: -x objective-c
 #cgo LDFLAGS: -framework CoreFoundation -framework Security
+#include <TargetConditionals.h>
 #include <CoreFoundation/CoreFoundation.h>
 #include <Security/Security.h>
-#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
+#if TARGET_OS_OSX && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
   typedef CFStringRef SecKeyAlgorithm;
   static CFDataRef SecKeyCreateSignature(SecKeyRef key, SecKeyAlgorithm algorithm, CFDataRef dataToSign, CFErrorRef *error){return NULL;}
   #define kSecKeyAlgorithmECDSASignatureDigestX962SHA1 foo()

misc/cgo/test/issue24161e1/main.go

@@ -9,9 +9,10 @@ package issue24161e1
 /*
 #cgo CFLAGS: -x objective-c
 #cgo LDFLAGS: -framework CoreFoundation -framework Security
+#include <TargetConditionals.h>
 #include <CoreFoundation/CoreFoundation.h>
 #include <Security/Security.h>
-#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
+#if TARGET_OS_OSX && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
   typedef CFStringRef SecKeyAlgorithm;
   static CFDataRef SecKeyCreateSignature(SecKeyRef key, SecKeyAlgorithm algorithm, CFDataRef dataToSign, CFErrorRef *error){return NULL;}
   #define kSecKeyAlgorithmECDSASignatureDigestX962SHA1 foo()

misc/cgo/test/issue24161e2/main.go

@@ -9,9 +9,10 @@ package issue24161e2
 /*
 #cgo CFLAGS: -x objective-c
 #cgo LDFLAGS: -framework CoreFoundation -framework Security
+#include <TargetConditionals.h>
 #include <CoreFoundation/CoreFoundation.h>
 #include <Security/Security.h>
-#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
+#if TARGET_OS_OSX && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101200
   typedef CFStringRef SecKeyAlgorithm;
   static CFDataRef SecKeyCreateSignature(SecKeyRef key, SecKeyAlgorithm algorithm, CFDataRef dataToSign, CFErrorRef *error){return NULL;}
   #define kSecKeyAlgorithmECDSASignatureDigestX962SHA1 foo()